CP2K Open Source Molecular Dynamics

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Calculation of the bandstructure of Si by means of DFT with different settings

connect to hypatia:

ssh -X EMPA-USER@jump1.empa.ch
ssh -X hypatia

module load python/2.7.12

go in the directory where you want to put the exercise and do:

cp /home/cpi/exercise_11.tar ./
tar -xvf exercise_11.tar
cd exercise_11

You will find a different directory for each TASK

Please have a look at this web page

http://materialscloud.org/sssp/

where pseudopotentials for different elements of the periodic table can be found. For each pseudopotential several convergence test have been made, the use of the data contained in this webpage can be in general trusted, but additional tests are always a good praxis

Please also have a look at the webpage of quantum-espresso to find a detailed description of input parameters

http://www.quantum-espresso.org/

TASK_0

The batch script run contain the instruction to run a quantum-espresso DFT calculaiton for a conventional cell of Si (ibrav=1 for simple cubic cell). As you can see in the file, 8 atoms are included in the cell of parameter a=5.43A. The primitive cell (ibrav=2 for fcc) would contain only 2 atoms and would not be cubic. The scirpt is ment to run a calculation to optimize the wavefuntion of the system and to compute the total energy. A sinlge k point, Gamma, is used for the summation over the Brillouin Zone.

edit the script run and identify the sections where

the lattice parameter is specified
the type of lattice (ibrav) is specified
the coordinates of the atoms are provided in crystal coordinates
the Monkhorst-Pack grid (in this case only Gamma point) is specifyed for the BZ sums
how many electrons do we have in the system?
how many occupied egigenvector do we have for each k-point (the occupation is printed in the output for each k-point after the energies of the eigenvalues belonging to the k-point

Submit the calculation to the queue

qsub run

Have a look to th eoutput generated: si.out

identify where the symmetry operations used by the code are listed
identify the k-points used during the calculations
find where the eigenvalues (provided in eV) for each k-point are printed
find the total energy of teh system

to find the total energy of the system you can also type:

grep "\!" si.out

to find the Fermi energy of the system you can also type:

grep "Fermi" si.out

TASK_0b, TASK_0c, TASK_1

The three tasks repeat the calculation of TASK_0 with a different sampling of the BZ in 0b a non shifted grid of 2x2x2 k-points is used, thus containing high symmetry points (so not ideal to have a accurate integration) in 0c the 2x2x2 grid is shifted and in TASK_1 a non shifted 3x3x3 grid is used.

have a look at the three different run files and submit all of them then write down the total energy that you get from the three different outputs

TASK_2

Here the run script contains teh data to run a calculation for a large Si cell There are 216 atoms corresponding to 3x3x3 of the conventional cell used in the previuos calculations

submit the calculation (it will take ~10 minutes to be completed) compare the total energy (THAT WE CALL E27)obtained in this calculation with the ones obtained in task_0,0b,0c,1

why the total energy obtained in TASK_1 is closer to E27/27 compared to the energies obtained in TASKS 0,0b,0c?
Compare the eigenvalues that you have now at the Gamma k-point with the eigenvalues you had on the different k-points for the calculation of TASK_1. All the eigenvalues obtained in TASK_1, that are subdivided in different k-points are now grouped in a single k-point.